Introduction: Clinical investigations of intraspinal stem cell therapies are underway for a range of neurological diseases. Originally considered entirely immuno-privileged, the CNS is now considered relatively privileged and immunological reactions to exogenously transplanted cell grafts have been demonstrated in mammalian models. From these observations, immunosuppression regimens have been employed clinically. However, graft rejection remains a significant risk and an assay to non-invasively monitor the immune response to transplanted intraspinal cell grafts is essential. We hypothesize that graft-specific host antibodies may be detected in the peripheral blood.
Methods: Ten minipigs received five intraspinal injections of 100,000 donor human neural progenitor cells. Five pigs received tacrolimus and five received no immunosuppression. Plasma was isolated from peripheral blood collected pre-transplant and serially post-transplant. Furthermore, plasma was collected from six patients with Amyotrophic Lateral Sclerosis enrolled in the Phase 1 trial at Emory (NCT01348451) receiving intraspinal injections of donor human neural stem cells. The patients received tacrolimus, mycophenolate mofetil, and basiliximab. Plasma was collected from three patients with naïve transplants and three patients with second transplants. Donor stem cells were incubated with collected plasma and then incubated with a fluorescent conjugated antibody specific to either pig or human IgG to measure the presence of graft-specific antibodies in the plasma. Relative mean fluorescent intensity (MFI) was measured with flow cytometry and compared to pre-operative baseline.
Results: A transient increase in graft-specific antibodies was detected one and two weeks post-operatively in pigs that did not receive immunosuppression. No increase was observed in the tacrolimus group. In patients, a trend showing a slight decrease in graft-specific antibodies was observed.
Conclusions: This method can be used to detect antibody-mediated graft rejection in vivo. Furthermore, it provides evidence for a decreased immune response to transplanted intraspinal stem cell grafts with immunosuppression.
Patient Care: This technique will allow clinicians to monitor the immune response to CNS stem cell therapy in vivo. Furthermore, it provides some preliminary evidence for the benefit of immunosuppression in the clinic.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Discuss the importance of immunosuppression in stem cell therapy
2) Identify assays for detecting the immune response to stem cell therapy